A problem found in lighted instrument panel displays such as those in use in land vehicles, watercraft and aircraft is that light emitted by the display exits through a wide range of angles. Some of this light can strike nearby reflective surfaces such as a windshield or cockpit windows and be reflected back towards the operator of the craft. While sunlight generally prevents such reflections from being visible during the day, they are often clearly visible at night. Such reflections can create a dangerous situation by distracting the operator or even obscuring the operator's view.
In addition to reflections from light emitted by the display, ambient light reflected from the viewing surface of the display toward the operator can obscure the display itself. The ambient light source can be, for example, light entering through a nearby window or reflections from a white shirt worn by the operator.
To eliminate the above indicated reflections, various types of enclosures, shrouds, and the like have been used to at least partially enclose or surround the display to prevent ambient light from falling directly on the front surface of the display and to control the angle of light emitted by the display itself. An example of the use of an enclosure is an instrument panel with one or more recessed displays. An example of a shrouded display is an automobile dashboard having a top portion of the dashboard, or brow, extending out over the display to prevent light, from the sun for example, from entering through the windshield and reflecting from the viewing surface of the speedometer towards the driver. The brow is also said to help prevent reflections from indirect sources such as the “white shirt” reflection described above.
A disadvantage to the use of enclosures, shrouds, brows, and the like to control ambient or emitted light is the extra weight and depth added to the instrument panel. Automobile manufacturers, for example, seek to reduce overall vehicle weight in order to increase fuel efficiency. Reducing the dashboard depth contributes to reduced vehicle weight. Reducing the depth of an instrument panel can also provide more usable space in the surrounding area.
It is also known to provide random structure or texture to the face of the display for use with browless instrument panels to help prevent distracting reflections from the front surface of the display. Such structure does not address reflections caused by light emitted by the display.
Light collimating film, typically comprising a series of micro-louver elements, acts to restrict the viewing angle of light transmitted by the film. It has been used in front of a display, for example on a computer monitor screen, to restrict the viewing angle so that only the person directly in front of the screen may view the contents of the display. Light collimating film has been used behind a liquid crystal display for the same purpose, for example, in a publicly available automatic teller machine (ATM) display. Use of light control film in these instances, however, limits the viewing angle in only one direction.
The combination of two adjacent sheets of light collimating film with their collimating axes orthogonal to each other disposed in front of a display has been reported, but this combination is unsatisfactory as below.